1. Field of the Invention
This invention relates to vehicles for transporting heavy loads and has particular reference to auxiliary wheel apparatus for assisting the usual front and rear vehicle wheels when transporting heavy loads.
2. Description of the Prior Art
Many vehicles, such as trucks, are intended to carry loads which exceed the safe carrying capacity of the usual vehicle wheels or which exceed the maximum load capacity of the wheels as authorized by law. This is especially true of concrete transporting trucks for carrying freshly mixed concrete to intended pouring sites. For example, a twelve cubic yard load of concrete carried by a typical concrete transporting truck weighs on the order of 48,000 pounds and this normally exceeds the legal allowable load carrying capacity for trucks of this type unless equipped with auxiliary load carrying means.
In order to satisfy load and safety requirements, concrete transferring trucks have usually heretofore been equipped with auxiliary load carrying wheels which are mounted to the rear of the conventional rear truck wheels. Such auxiliary wheels are mounted to freely caster about vertical axes so that they may track or roll in alignment with the truck since this reduces sidewise skidding and consequent wear of the auxiliary wheel tires, especially when the truck is turned in different directions. However, because of the heavy loads carried by such trucks, they tend to sway from side to side while travelling along a roadway, particularly if such roadway is uneven. If such swaying becomes excessive, it can result in overturning of the truck. Further, if one of the auxiliary wheels should experience a blow-out or other damage to its tire, the latter will tend to drag the truck to one side, also with the possibility of causing the truck to overturn.
It has been found that some reduction in sidewise swaying can be effected by causing the auxiliary wheels to "tow-in", i.e. to cause the general planes of the auxiliary wheels to converge and to intersect at some distance ahead. However, such tow-in causes excessive tire wear and difficulty in steering.
Accordingly, a principal object of the present invention is to provide means for reducing the tendency of heavily laden vehicles to sway sideways while they are travelling along a roadway.
Another object is to provide means for reducing the possibility of a heavily laden vehicle going out of control due to a tire blow-out or other damage to one of the supporting wheels.
Another object is to reduce the wear on the tires of auxiliary load supporting wheels of the aforementioned type.
A further object is to provide a device capable of accomplishing the above objects which is simple, reliable and economical to manufacture.
According to the invention, the free turning auxiliary load carrying wheels of a vehicle of the above type have their spindles pivotally supported for a castering movement about vertical axes by an axle mounted on a frame structure. The spindles are interconnected by a transversely extending tie rod and stressed springs are mounted between the tie rod and the axle to yieldably hold the auxiliary wheels in planes normally extending parallel to the length of the vehicle. When the truck is turned, the auxiliary wheels swivel or caster about their spindle pivots to enable such wheels to track without skidding sideways, during which time one of the springs is further stressed and the other is relaxed. Then, when the vehicle subsequently returns to travel in a straight line, the stressed spring will aid in returning and maintaining the auxiliary wheels in planes parallel to the length of the vehicle and will also aid in overcoming any tendency for the vehicle to sway from side to side.